This study aims to evaluate the effectiveness of a housing intervention for inadequately housed families under investigation by the child welfare system, as well as to understand the mechanisms and conditions through which the program most benefits child development. The intervention - the Family Unification Program (FUP) - is a Housing and Urban Development (HUD) initiative that provides Housing Choice Vouchers (Section 8) to families whose inadequate housing risks out-of-home placement. The study proposes to take advantage of a natural experiment that randomly provides FUP services to families (n = 100) who will be compared to a child welfare services-as-usual control group (n = 100). Oversampling will occur in both conditions to account for voucher uptake failure and attrition. The study will obtain two baseline assessments before housing services and then re-assess at 6-, 12-, and 24-months post-baseline for a total of five time points. Caregivers and their children will be administered a panel survey. The study will test a number of hypotheses: 1) it is hypothesized that families receiving housing services will report greater family stability - as indicated by residential stability, housing quality, daily routines, noise and confusion, caregiver mental health, caregiver separations, and school changes - compared to child welfare services-as-usual; 2) it is predicated that the housing intervention will have a significant positive impact on child physical and mental health, academic achievement, and developmentally adaptive behavior, relative to services-as-usual; 3) we hypothesize that positive effects on child development associated with housing services will function through reductions in family stability; 4) we hypothesize that families from less cohesive and more violent neighborhoods will gain less from the intervention; 5) we hypothesize that the housing intervention will have its greatest impact on families who are most unstable at baseline; 6) it is theorized that the housing intervention will have greater positive effects for younger children. The rigorous design enables strong scientific investigation of how FUP functions and whether intervention operates similarly across multiple levels of context. This project intends to improve understanding of the mechanisms of the FUP intervention to provide a stronger basis to build evidence-based service models and public policy. PUBLIC HEALTH RELEVANCE: This study takes advantage of a natural experiment to test the effectiveness of an intervention for inadequately housed families under investigation for child maltreatment. The proposed study simultaneously aims to inform social policy and service provision in the child welfare system, while investigating the processes involved in the relationship between family instability and adverse child development among at-risk families.